1. Field of the Invention
The present invention relates to the drilling and completion of subterranean wells. The present invention relates to a clamp for gripping and suspending a tubular string in a borehole.
2. Description of the Related Art
A spider is an apparatus used for gripping and supporting long strings of pipe in a borehole, such as casing strings. A spider is generally mounted in the floor of drilling rig, and has a generally circumferential arrangement of slips that grip and hold the casing tighter as the weight of the casing is transferred to the slips. The spider is operable to disengage from and release the casing as the casing is lifted relative to the spider. An elevator attached to a hoist may be used to raise and lower the casing, and the elevator cooperates with the spider.
A spider typically includes a tapered bowl and a plurality of arcuate wedge-shaped slips held in a generally circumferential arrangement within a tapered bowl. The slips are normally moved to ride along the tapered surface of the spider bowl. The slips are adapted for being engaged and disengaged with the casing while maintaining contact with the tapered bowl. When the slips are raised, they move up and radially outward to increase the size of the opening in which the casing is received. Conversely, when the slips are lowered, the slips move down and radially inward to engage and support the casing. Frictional engagement between the casing and the slips draws the slips downward and inward along the tapered bowl and into tighter gripping engagement with the casing.
Spiders are generally adapted for supporting long, casing strings that may weigh in excess of 400,000 pounds (181,500 kg). To support the weight, spiders are generally made to be quite massive, with as many as 12 cooperating slips. The operation of spiders can therefore be time consuming. Spiders rely on self-tightening; that is, the weight of the casing string pulls the slips downwardly and inwardly along the spider bowl to bear firm against the casing. Insufficient engagement may result if the casing string is short and the casing string is too light too forcibly set the slips.
What is needed is an improved device for supporting relatively light tubular strings in a borehole. The improved device may allow tubular strings to be more quickly and easily assembled or disassembled, particularly when handling lighter tubular strings that do not require the load-bearing capacity of a conventional spider.